These vascular bundles have peripheral or outer phloem and inner or central xylem
I. Amphicribal vascular bundles
II. Collateral vascular bundles of stem
III. Radial vascular bundles
Collateral vascular bundles of stems and amphicribal vascular bundles of pteridophytes stems have peripheral phloem and inner or central xylem. Radial vascular bundles have xylem and phloem in the same perimeter but on different radii.